How do I stop second-guessing myself after a work gap?

You are back in the work, and a voice keeps telling you that you are behind on everything. Notice that it says everything, which is how you know it is fear talking, not fact. Fear speaks in totals. The truth is always more specific and more manageable. You did not lose what you know. Skills go quiet after a break, but they come back fast once your hands and mind start using them again. Some things did move on while you were away, and that is normal in any field. But that is a short list to catch up on, not proof that you have fallen hopelessly behind. The second-guessing is the rust, not the blade. Make the vague fear concrete. Write down the specific things you actually need to relearn or update. It will be a shorter list than the dread suggested, and a list can be worked through one item at a time. Confidence comes back through doing, not through waiting to feel ready.